A national vaccine surveillance program that Vanderbilt University is a part of has identified a significant shift in the most common cause of childhood diarrhea.

A study released March 21 in the New England Journal of Medicine (NEJM), finds that norovirus (sometimes called the Norwalk virus) is now the leading cause of childhood diarrhea. Rotavirus once caused 90 percent of cases of childhood diarrhea, but rates have steadily declined since a vaccine came into widespread use in 2006.

The New Vaccine Surveillance Network (NVSN), which includes Vanderbilt, the University of Rochester and Cincinnati Children’s Hospital, tracks a number of viral illnesses and the impact of vaccination.

Kathryn Edwards, M.D., the Sarah H. Sell and Cornelius Vanderbilt Chair in Pediatrics and director of the Vanderbilt Vaccine Research Program, served as director of the Vanderbilt arm of the NVSN during this study to examine the causes of childhood diarrhea from 2008 to 2010.

“It is important to note that even though the threat of rotavirus is greatly reduced, our study shows the intensity and burden of norovirus has remained unchanged,” Edwards said.

Kathryn Edwards, M.D.

In the NEJM study, the researchers tracked more than 141,000 children under age 5. Children with diarrhea were treated in hospitals, emergency departments and outpatient medical offices.

Lab testing confirmed the presence of norovirus and rotavirus in 1,295 cases. Norovirus was detected in 21 percent of cases, while rotavirus was identified in only 12 percent. Edwards acknowledged this study reinforces the great success of rotavirus vaccination programs.

Each year nearly a half million children die worldwide from the effects of rotavirus. Edwards said while global health efforts continue to increase the availability of rotavirus vaccine in developing nations, it is time for researchers to shift their focus to developing a norovirus vaccine.

“I think this speaks to the fact there is a large burden of norovirus and a great need for a vaccine to prevent it. Young children and elderly people are at highest risk for norovirus illness,” Edwards said

The researchers estimate that in 2009 and 2010, as many as 1 million young children and infants required medical treatment for norovirus illness, at a cost of approximately $270 million. The younger the child, the harder the virus hits.

About half of all cases requiring medical treatment were among children age 6 months to 18 months.

Infants and 1-year-old children were more likely to be hospitalized than older children. Norovirus infections cause sudden onset of intense vomiting and severe diarrhea that can last three days. Dehydration is the most common serious health concern.

The virus is spread through close contact or through contact with infected objects or surfaces. Currently, the best ways to reduce the risk of norovirus infection are through proper hand washing, safe food handling and proper cleaning of surfaces.